Depressurization of arc lamps

ABSTRACT

A closed cycle depressurization system including a lamp envelope for containment of a discharge gas at greater than atmospheric pressure in communication with a gas storage and depressurization chamber. A substantially transparent material, potentially frangible at said pressure forms at least a portion of the envelope. In one embodiment, depressurization is effected by externally cooling the walls of the chamber and in a second embodiment the chamber contains a gas adsorbent which adsorbs gas to reduce the pressure in the lamp envelope to the desired safe nonoperating level. Repressurization is accomplished by raising the temperature of the chamber and the stored gas and recycling the gas to the envelope.

United States Patent Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Attorney-Lindenberg and Freilich ABSTRACT: A closed cycle depressurization system including a lamp envelope for containment of a discharge gas at greater than atmospheric pressure in communication with a gas storage and depressurization chamber. A substantially transparent material, potentially frangible at said pressure forms at least a portion of the envelope. 1n one embodiment, depressurization is effected by externally cooling the walls of the chamber and in a second embodiment the chamber contains a gas adsorbent which adsorbs gas to reduce the pressure in the lamp envelope to the desired safie nonoperating level. Repressurization is accomplished by raising the temperature of the chamber and the stored gas and recycling the gas to the envelope.

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INVENTOR.

CHARLES G. MILLER ATTQRNEYS DEPRESSURIZATION or ARC LAMPS ORIGIN OF THE INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to depressurization of gas envelopes containing frangible portions and more particularly this invention relates to a closed cycle system for depressurization and repressurization of xenon compact-arc lamps.

2. Description of the Prior Art Many vessels, e.g., photochemical reactors or lamps have portions of their body formed of tensilely frangible materials such as quartz for necessary reasons such as light input or output. Yet, these vessels are operated at internal pressures likely .to cause failure of the weaker portion.

The most prevalent kw. xenon compact-arc lamp in current use has a quartz envelope which is pressurized to an internal pressure of approximately 50 p.s.i.g. at room temperature, and at operating temperature the pressure increases to approximately 160 p.s.i.g. Lamp use has been limited by envelope fragility, short life expectancy and unexpected catastrophic failure of the envelope both during operation and when cold.

For these reasons the lamps have been transported in special containers and safety equipment must be worn by personnel in the vicinity of these lamps. The safety equipment definitely limits dexterity and increases the difficulty in cleaning, aligning, and installing the lamp in a reflector.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a method and apparatus for increasing the safety in handling and operating gas containing envelopes.

Yet another object of the invention is to provide a compact, efficient and simple arrangement for reducing breakage, extending operating life, and increasing the safety in the operation of high-pressure xenon-containing arc lamps.

A still further object of the invention is the provision of a system for depressurizing xenon arc lamp envelopes to a safe level and for readily repressurizing the envelope before the next period of operation, without introduction of impurities into the envelope. I

These and other objects and many attendant advantages of the invention will become apparent as the description proceeds.

In accordance with the invention, a high-pressure vessel containing at least one frangible portion is cyclically operated by pressurizing the vessel with gas and operating during a first period at a high pressure. During nonoperating periods, the vessel is depressurized to a safe level by removing the gas from the vessel and directly delivering the gas to a storage container. The gas is pumped to and depressurized within the con tainer by condensation or adsorption and before the start of the next operating period the gas is pressurized to high pressure by raising the temperature of the container and the stored gas and recycling the gas to the envelope.

An arc discharge lamp system of the invention comprises a high-pressure gas envelope for containment of said gas at a high pressure. An anode and cathode are supported within the envelope. The ends of the anode and cathode are separated to form a discharge gap. Gas storage containing means for depressurizing said envelope are selectively communicable with said envelope and means are associated with said storage means for increasing the pressure therein. In one embodiment the depressurizing means comprises means for lowering the temperature of the walls of said storage means and in another embodiment the depressurizing means comprises an adsorbent for binding means comprises an adsorbent for bind the gas contained within the envelope.

The invention will now become better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a sectional view of a first embodiment of a closed cycle depressurization system according to the invention;

FIG. 2 is a sectional view of a second embodiment of a closed cycle system of the invention;

FIG. 3 is a schematic view of the embodiment of FIG. 2 modified for use under water; and

FIG. 4 is a partially broken-away perspective view of an intemal reflector-sealed beam lamp embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, the first embodiment of the invention generally comprises a lamp 10, a gas storage chamber 12, and tubing 14 connecting the lamp 10 with the chamber 12.

The lamp Ill includes a transparent envelope l6, suitably formed of quartz. A flange I8 is attached to the envelope I6 adjacent each open end thereof. Each end surface of the envelope is relieved to form an inner ridge for receiving an O- ring 20. Lamp ends 22 and 24, having a plurality of apertures adjacent the outer periphery are attached to the lamp envelope 16 by means of a plurality of bolts 26 extending through the apertures and correspondingly located holes in flange l8 and are secured by means of nuts 28. The interfaces between the ends 22 and 24 and the lamp envelope 16 are sealed by means of the O-rings 20.

The lamp ends 22 and 24, suitably formed of brass, support an anode 30 and a cathode 32 facing each other across a discharge gap 34. In another conventional design of short-arc, high-intensity xenon lamps, the electrodes are held in place by the quartz envelope be means of a quartz to metal seal between the envelope and the electrodes.

The anode is preferably a hollow copper tube 36 which may be tipped with tungsten. An annular coolant passage may be formed in the interior of tube 36 by means of a pipe 38 extending through end 22 into the interior of tube 36 to form an annular water passage 40 which communicates with a water inlet 42 again extending through lamp end 22. Cool water entering inlet 42 passes through the annular space 40 to cool the hot end of the anode 30 and enters pipe 38 and passes out through water outlet 44.

The cathode is in the form of a hollow tube 46 suitably formed of thoriated tungsten inserted into a hollow stud 48 extending from the brass end plate 24. A cooling water inlet 50 inserted through the end plate 24l delivers water to an annular cooling passage 52. An outlet pipe 5% removes water from the central pipe 55.

A gas fill tube 56 is inserted through end plate 24 and communicates with the interior of the quartz envelope H6. The fill tube 56 is attached through a tee connection 58 to a first branch 60 which may be pinched off at 62 or may contain a pressure indicating valve, not shown. The second branch 64 contains a shutoff valve 65, and communicates at its outer end with the interior of storage container 605. The exterior wall of container 66 may be surrounded with a jacket 70. A fill tube 72 containing a two-way valve 74 can 'be connected through pipe joint 76 to a cryogenic source 78 such as a container of liquid nitrogen having an outlet tube 77 and outlet valve 79.

The lamp is assembled by bolting the end plates 22 and 24 to the flanges 13. Electrical leads 61 and 63 are connected to the brass end plates 22 and 24 and to a power source, not shown. The shutoff valve 65 is placed in open position and sufficient operating gas which may be xenon, or any of the gases chosen from the class of neon, xenon, argon, krypton or the mixtures thereof, is introduced into the evacuated and moisture-free interior of the envelope l6 and storage con tainer 66 through the side arm 60 of the gas fill tube 56 such that the equilibrium pressure at ambient temperature is about 50 p.s.i.g. The end of arm 60 is then pinched off at 62 or a pressure-indicating gauge is installed at that location.

During operation, water is circulated through both of the electrode-cooling passages. The lamp is operated at 20 kw. input which develops an internal pressure of about 160 p.s.i.g. Even higher inputs and gas pressures are possible and therefore depressun'zation as a safety measure would be of considerably more importance. Afterthe operating lighting period, power to the-electrodes is terminated.

The outlet tube 77 and a liquid nitrogen tank 78 is connected to joint 76 and valves 79 and 74 are opened to fill the cryogenic jacket 70 with liquid nitrogen. Alternatively, liquid cryogenic material may be poured into jacket 70. Shutoff valve 65in branch 64 is opened and the condensation of the xenon gas within storage chamber 66 creates a pressure differential which tends to pump xenon gas out of the quartz envelope 16. It is convenient to close valve 65 when the pressure in envelope 16 is about 5 p.s.i.g., to be sure that there are no undesirable reverse forces on the O-ring system 20. The xenon condenses to form a snowlike solid within the chamber 66. When valve 65 is turned to its closed position, valves 79 and 74 may be closed and the tank 78 removed from the joint 76. When valve 74 is opened the temperature of the storage chamber will rise to ambient temperature. Immediately before the next period of operating the lamp, shutoff valve 65 is opened and the contents of chamber 66 will expand and the envelope will be repressurized with xenon gas to a pressure of 50 p.s.i.g. Valve 65 is again closed and the lamp operated. In this particular configuration the internal volume of the lamp envelope is about 1,600 cc. The envelope can be depressurized to a safe level utilizing a storage container 66 having a volume of about 75 cc.

The arrangement illustrated in the embodiment of FIG. 2 permits use of a smaller storage chamber which need not be of high-pressure resistant material such as the chamber 66, and dispenses with the need for liquid nitrogen, or other cryogenic fluid. Since the lamp structure is identical to that shown in FIG. I, the details of the lamp are omitted in this description. The apparatus of FIG. 2 includes a lamp having an envelope 16, a storage chamber 80 filled with a gas adsorbent material 82 and a heating coil 84 encircling the chamber 80 for raising the temperature of the contents thereof. The circuit for the heating coil 84 contains an energy source 86 and a switch 88.

The storage chamber 80 having a volume of 30 cc. containing about 30 grams of activated charcoal has sufi'icient volume and adsorbtivity to reduce the pressure of the envelope 16 to a safe level during nonoperating periods of the lamp. Other suitable adsorbents for use in the embodiment of FIG. 2 are molecular sieves such as zeolites which are alkali or alkaline earth metal aluminum-silicates.

The adsorbent container of FIG. 2 can be about one-half or lrss compared to the volume of the cryogenically cooled chamber of the embodiment of FIG. I and have satisfactory depressurization capability. Furthermore, the necessity of lowering the chamber temperature by refrigeration to effect depressurization is obviated because of the inherent ability of the adsorbent to bind and hold the gas at room temperature. Repressurization, however, requires application of heat to drive the xenon gas from the charcoal or other adsorbent which is effected by a heating coil 85 wrapped around the chamber. When switch 88 is closed the energy source 86 is placed in circuit with the heating coil and the heat developed raises the temperature of the chamber walls and of the adsorbent 82. The adsorbent has less ability to hold gas at higher temperature and releases the gas from the surface thereof. When the lamp has been repressurized to the desired level, valve 65 is closed and energy source 86 may be disconnected.

After an operating period the lamp envelope is permitted to cool to ambient temperature before opening valve 65. When valve 65 is opened the xenon gas at the higher pressure in envelope I6 enters the lower pressure container 80. The gas is adsorbed on the surfaces of the activated charcoal or other adsorbent 82 which continues to create a low-pressure driving force pumping the gas out of envelope 16. When the gas pressure within the envelope 16 has been reduced suitably to a value slightly above atmospheric, such as 5-10 p.s.i.g., valve 65 is closed. It is not necessary, or desirable to reduce the pressure in envelope 16 below this level since the force of the atmosphere may create excessive stresses on the O-ring seals and tend to damage them or to permit leakage of the xenon gas or introduction of impurities.

The embodiment of FIG. 2 employing an adsorbent effective to depressurize the lamp envelope at room temperature is more readily adaptable to remote operation as compared to the apparatus of FIG. 1, which requires use of a refrigerant. Furthermore, liquid nitrogen is consumed in the process of FIG. I and therefore involves the cost of replenishment each time depressurization is necessary. Moreover, cryogenic liquids such as liquid nitrogen, involve substantial complications and precautions in handling and use.

Pressurized arc-discharge lamps modified according to the invention may be quite advantageously utilized for underwater illumination as illustrated in FIG. 3. Quartz is quite strong under compression but has much less strength under tension. When the lamp envelope is immersed in water, the hydrostatic pressure of the water exerts compressive forces on the envelope. As the water depth is increased the internal pressure at which the lamp may be operated correspondingly increases. Each 34 foot head of water exerts one atmosphere of pressure on the envelope and thus would allow increasing the internal pressure by one atmosphere. The brightness of the output beam emitted from the lamp increases as the internal pressure increases.

In the embodiment of the lamp shown in FIG. 3 full advantage may be taken of the depth of the lamp under water by providing means for varying the internal pressure of the lamp. In one form, the internal pressure of the lamp envelope is varied by means of a reservoir 102 surrounded with a heating coil 104. The circuit for the heating coil includes a switch I 16, an energy source l 18 and a rheostat 120. The reservoir I02 is filled with gas adsorbent particles and connected to the envelope through a tube 106 containing a metering valve 108. The metering valve is driven by a solenoid 1 l0 and is separate ly actuatable by means of switch 1 11. The valve and reservoir assembly are housed in a waterproof enclosure 112.

The anode and cathode water-cooling circuits may be supplied with coolant in a closed cycle from a single pump 130. The input side of the pump is connected through a tee connection 131 to the output tubes 133 from both lamp electrodes. The output side of pump 130 is connected through a tee connection I36 to the coolant input tubes I38 to the lamp electrodes.

As the depth of the lamp 100 below the surface of the body of water is increased, the heater switch 116 is closed and the rheostat 120 adjusted to raise the temperature of the reservoir 102 and of the gas adsorbent stored therein to drive more gas from the adsorbent. After the desired temperature is reached the solenoid switch 111 is closed and the solenoid opens valve 108. Additional discharge gas enters envelope 100. When the lamp is again energized the output beam will be correspondingly brighter.

The depressurization system of the invention is also applicable to pressurized lamp housings, only a portion of which is potentially frangible under pressure. Obviously, only the window portion of the lamp need be transparent while the other portions may be constructed of higher structural strength materials such as metal or ceramic. An internal reflector and internal depressurization system may be incorporated readily within the envelope of this type of lamp.

Referring now to FIG. 4, the particular lamp 200 illustrated is a sealed beam illuminator having a narrow neck portion 202 adapted for insertion into a socket, not shown. In this configuration, it is preferable to include the gas depressurization reservoir 204 within the lamp envelope.

The lamp envelope can be formed of a high-strength ceramic-metallic envelope containing an anode 206 and a cathode 208, a transparent window 210 suitably formed of sapphire, quartz or other transparent material and an integral prealigned reflector 212. Aligning the electrodes parallel to the beam axis eliminates the problem of electrode beam shadowing and distortion.

The envelope assembly illustrated is formed in three parts. The metallic cathode and reflector assembly 2114 and the metallic anode and window assembly 216 are joined to a ceramic ring 218. The first assembly 2M includes the neck portion 202 joined to the reflector 212 which terminates in a flange 222 brazed to the ceramic ring 218. The cathode 21th is mounted within the neck 202 and protrudes outwardly into the envelope. The end 224 of the cathode is spaced from the end 226 of the anode to form a discharge gap 228.

The gas reservoir 204 is disposed within the neck 202 below the illuminator to avoid shadowing effects. The gas reservoir 204 is in the form of a tube filled with gas adsorbent. At least one end 230 of the tube is formed of a gas-permeable, adsorbent impervious structure such as a layer of glass wool covered by a metal screen 232 attached to the wall of the reservoir. The discharge gas may be driven from the adsorbent by heating the reservoir from externally applied energy. Preferably, a heating coil 234 surrounds the reservoir 2% and the coil is powered by a energy source, not shown.

The anode-window assembly comprises a window rim M supporting the window 210. The rim is attached to an enlarged flange 242 which is brazed to the outer end of the ceramic ring 218. The anode 206 is supported in alignment with the beam axis by means of a set of radial straps 246 one end of each being attached to the base of the anode and the other end to the flange 242. Electrical input is provided to the anode through the flange 242.

Just before illumination is desired, the heating coil 2% is energized to release sufficient gas for lamp startup. Then the electrodes are energized and operated. Since the amount of gas adsorbed decreases with temperature during operation, the hot environment provided by the discharge will supplement the heating coil 234 in releasing discharge gas from the adsorbent. After the lamp operation is tenninated, the lamp envelope will cool and the xenon gas will be readsorbed by the adsorbent to depressurize the lamp envelope to a safe level.

Molecular sieve zeolite adsorbent particles in the form of small diameter rods have been found to operate very effectively in the dcprcssurization system of the invention. The rodshaped particles pack to a compact mass of high porosity. The molecular sieve rods which may be formed of zeolite are strong and do not exhibit any substantial tendency to break, flake or crumble.

The depressurized lamp systems according to the invention can be used in the same applications currently using high-intensity arc lamps. As examples of numerous applications, these lamps can be utilized as microscope stage illuminators, in photoanalytical instruments, or as a spectrometer light source. In materials processing the lamps can be used for radiant heating. They also find use in initiation of chemical reactions, actinic flash photolysis, and light and color matching and measurement. The lamp will also find use in photography, beacon communications, tracking and in display and projection systems as in motion picture projectors. Recently, xenon lamps are being utilized as scarchlights mounted on land vehicles or on helicopters.

It is to understood that only preferred embodiments of the invention have been illustrated and that numerous substitutions, alternations and modifications are permissable without departing from the scope of the invention as defined in the following claims.

What is claimed is:

l. A high-pressure arc illumination system comprising:

a lamp envelope for containing a discharge gas;

a substantially transparent material, potentially frangible at greater than atmospheric pressure fomiing at least a portion of the envelope;

electrode arc discharge means supported within the envelope;

a discharge gas storage reservoir;

a first means coupling the envelope to the reservoir forming a closed, gas right system for transferring discharge gas from the envelope for storage in said reservoir in order to depressurize the envelope to a safe level;

a body of discharge gas received within said system in an amount sufficient to pressurize said envelope to a was sure greater than atmospheric during nonoperation of said lamps;

a body of discharge gas absorbent contained within said reservoir in an amount sufiicient to adsorb the discharge gas at room temperature to depressurize said envelope to a pressure below atmospheric; and

heater means connected to said reservoir and independent of said electrode discharge means for operation during off periods of said electrode discharge means to desorb gas from said adsorbent and return gas to the envelope at a pressure greater than atmospheric before startup up of said electrode discharge means.

2. A system according to claim 11 wherein the adsorbent is selected from the class of materials consisting of activated charcoal and molecular sieves.

3. A system according to claim ll wherein the discharge gas consists of a gas selected from the group consisting Neon, Argon, Krypton, Xenon and their mixtures.

d. A system according to claim ll wherein the reservoir is contained within said envelope.

5. A system according to claim ll wherein the reservoir is disposed external to the envelope and the system includes means for selectively connecting the reservoir and the envelope.

6. A system according to claim 5 in. which the envelope is connected to the reservoir through a tube containing a shutoff valve.

7. A system according to claim l in which said heater means includes control means for variably adjusting the operating pressure in the envelope.

8. A system according to claim 7 in which the control means comprises a variable heater for the reservoir and means for selectively controlling the power input to said heater.

9. in combination:

a vessel containing a gas at a pressure above atmospheric, at least a portion of the vessel being potentially frangible at said pressure;

lower pressure gas depressurizing means communicating with said vessel including a container housing a body of gas adsorbent in an amount sufficient to adsorb at room temperature gas from said vessel to depressurize said vessel to below atmospheric pressure; and

means for increasing the pressure of the gas within the depressurizing means for repressurizing said envelope to above atmospheric pressure comprising heater means connected to said container for heating said adsorbent to desorb said gas.

lltl. A method of operating a high-pressure, arc discharge lamp comprising the steps of:

connecting a lamp envelope to a discharge gas storage container to form a gastight closed system;

filing the lamp envelope with discharge gas at a first pressure greater than atmospheric, said envelope being potentially frangible at said first pressure;

operating said lamp at a higher pressure than said first pressure;

removing said gas from said envelope: during nonoperating periods by transferring at least a portion of the gas to the storage container to effect a depressurization of the envelope to a pressure below said first pressure;

depressurizing the gas within the container to a pressure substantially below said first pressure; and

repressurizing the gas within the container and recycling it to the envelope to pressurize the envelope to the first pressure before the start of the next. operating period for the lamp.

11. A method according to claim 10 wherein the gas is depressurized in said container by applying a coolant to the outside walls of said container to condense at least some of the contained gas.

12. A method according to claim 10 wherein the gas is depressurized within said container by adsorption of at least some of the contained gas on a body of gas adsorbent present in said container and capable of adsorbing sufficient amount of said gas at room temperature to depressurize said envelope to a pressure considerably below said first pressure.

13. A method according to claim 12 in which the adsorbent is selected from the group consisting of activated charcoal and molecular sieves.

14. A method according to claim 13 wherein said contained gas is repressurized by heating said container.

15. A method according to claim 10 in which the internal pressure of the envelope is controlled by selectively heating the reservoir to higher temperatures to deliver additional quantities of discharge gas to the envelope.

16. A method according to claim 10 in which said lamp is operated under water and the internal pressure of the envelope is adjusted to a value approximately equal to the hydrostatic pressure exerted by the surrounding water on the envelope.

17. A compact arc lamp illumination apparatus comprising in combination:

a lamp envelope for containing a discharge gas at a first pressure greater than atmospheric pressure during nonoperation of said lamp;

a substantially transparent material, potentially frangible at said pressure forming at least a portion of said envelope;

a pair of electrodes supported within said envelope for forming a high-pressure arc therebetween when discharged;

discharge means connected to said electrodes for operation of said lamp when said envelope is pressurized to said first pressure;

a discharge gas reservoir container disposed external to said envelope;

a body of gas adsorbent disposed within said container in an amount sufficient to adsorb said gas at room temperature to depressurize said container to a pressure substantially below said first pressure;

conduit means connecting said envelope to said container to fonn a gastight closed system;

a body of discharge gas consisting of a member selected from the group consisting of Neon, Xenon, Krypton, Argon and mixtures thereof received in said system in an amount sufficient to pressurize said envelope to at least said first pressure at room temperature;

valve means disposed in said conduit having an open position placing said envelope and container in communication, and a closed position placing said envelope and container out of communication; and

heater means connected to said container for heating said adsorbent to desorb said gas and pressurize the envelope to at least said first pressure when said valve is in open position and said discharge means are off.

18. An apparatus according to claim 17, in which said discharge gas consists of xenon and said adsorbent is selected from the group consisting of activated charcoal and a molecular sieve.

19. An apparatus according to claim 17 in which said envelope has at least one aperture, a metal lamp end is sealingly received over said aperture, one of said electrodes are supported on said lamp end and said conduit means is connected to the interior of said envelope through said lamp end. 

1. A high-pressure arc illumination system comprising: a lamp envelope for containing a discharge gas; a substantially transparent material, potentially frangible at greater than atmospheric pressure forming at least a portion of the envelope; electrode arc discharge means supported within the envelope; a discharge gas storage reservoir; a first means coupling the envelope to the reservoir forming a closed, gas right system for transferring discharge gas from the envelope for storage in said reservoir in order to depressurize the envelope to a safe level; a body of discharge gas received within said system in an amount sufficient to pressurize said envelope to a pressure greater than atmospheric during nonoperation of said lamps; a body of discharge gas absorbent contained within said reservoir in an amount sufficient to adsorb the discharge gas at room temperature to depressurize said envelope to a pressure below atmospheric; and heater means connected to said reservoir and independent of said electrode discharge means for operation during off periods of said electrode discharge means to desorb the gas from said adsorbent and return gas to the envelope at a pressure greater than atmospheric before startup up of said electrode discharge means.
 2. A system according to claim 1 wherein the adsorbent is selected from the class of materials consisting of activated charcoal and molecular sieves.
 3. A system according to claim 1 wherein the discharge gas consists of a gas selected from the group consisting Neon, Argon, Krypton, Xenon and their mixtures.
 4. A system according to claim 1 wherein the reservoir is contained within said envelope.
 5. A system according to claim 1 wherein the reservoir is disposed external to the envelope and the system includes means for selectively connecting the reservoir and the envelope.
 6. A system according to claim 5 in which the envelope is connected to the reservoir through a tube containing a shutoff valve.
 7. A system according to claim 1 in which said heater means includes control means for variably adjusting the operating pressure in the envelope.
 8. A system according to claim 7 in which the contRol means comprises a variable heater for the reservoir and means for selectively controlling the power input to said heater.
 9. In combination: a vessel containing a gas at a pressure above atmospheric, at least a portion of the vessel being potentially frangible at said pressure; lower pressure gas depressurizing means communicating with said vessel including a container housing a body of gas adsorbent in an amount sufficient to adsorb at room temperature gas from said vessel to depressurize said vessel to below atmospheric pressure; and means for increasing the pressure of the gas within the depressurizing means for repressurizing said envelope to above atmospheric pressure comprising heater means connected to said container for heating said adsorbent to desorb said gas.
 10. A method of operating a high-pressure, arc discharge lamp comprising the steps of: connecting a lamp envelope to a discharge gas storage container to form a gastight closed system; filing the lamp envelope with discharge gas at a first pressure greater than atmospheric, said envelope being potentially frangible at said first pressure; operating said lamp at a higher pressure than said first pressure; removing said gas from said envelope during nonoperating periods by transferring at least a portion of the gas to the storage container to effect a depressurization of the envelope to a pressure below said first pressure; depressurizing the gas within the container to a pressure substantially below said first pressure; and repressurizing the gas within the container and recycling it to the envelope to pressurize the envelope to the first pressure before the start of the next operating period for the lamp.
 11. A method according to claim 10 wherein the gas is depressurized in said container by applying a coolant to the outside walls of said container to condense at least some of the contained gas.
 12. A method according to claim 10 wherein the gas is depressurized within said container by adsorption of at least some of the contained gas on a body of gas adsorbent present in said container and capable of adsorbing sufficient amount of said gas at room temperature to depressurize said envelope to a pressure considerably below said first pressure.
 13. A method according to claim 12 in which the adsorbent is selected from the group consisting of activated charcoal and molecular sieves.
 14. A method according to claim 13 wherein said contained gas is repressurized by heating said container.
 15. A method according to claim 10 in which the internal pressure of the envelope is controlled by selectively heating the reservoir to higher temperatures to deliver additional quantities of discharge gas to the envelope.
 16. A method according to claim 10 in which said lamp is operated under water and the internal pressure of the envelope is adjusted to a value approximately equal to the hydrostatic pressure exerted by the surrounding water on the envelope.
 17. A compact arc lamp illumination apparatus comprising in combination: a lamp envelope for containing a discharge gas at a first pressure greater than atmospheric pressure during nonoperation of said lamp; a substantially transparent material, potentially frangible at said pressure forming at least a portion of said envelope; a pair of electrodes supported within said envelope for forming a high-pressure arc therebetween when discharged; discharge means connected to said electrodes for operation of said lamp when said envelope is pressurized to said first pressure; a discharge gas reservoir container disposed external to said envelope; a body of gas adsorbent disposed within said container in an amount sufficient to adsorb said gas at room temperature to depressurize said container to a pressure substantially below said first pressure; conduit means connecting said envelope to said container to form a gastight closed system; a body of discharge gas consistinG of a member selected from the group consisting of Neon, Xenon, Krypton, Argon and mixtures thereof received in said system in an amount sufficient to pressurize said envelope to at least said first pressure at room temperature; valve means disposed in said conduit having an open position placing said envelope and container in communication, and a closed position placing said envelope and container out of communication; and heater means connected to said container for heating said adsorbent to desorb said gas and pressurize the envelope to at least said first pressure when said valve is in open position and said discharge means are off.
 18. An apparatus according to claim 17, in which said discharge gas consists of xenon and said adsorbent is selected from the group consisting of activated charcoal and a molecular sieve.
 19. An apparatus according to claim 17 in which said envelope has at least one aperture, a metal lamp end is sealingly received over said aperture, one of said electrodes are supported on said lamp end and said conduit means is connected to the interior of said envelope through said lamp end. 